1. Field of the Invention
The present invention generally relates to systems for adjusting the relative positions of machine and tool parts using lead screw drive mechanisms and, more particularly, is concerned with a lead screw piezo nut positioning device and a piezo nut positioner assembly thereof.
2. Description of the Prior Art
Lead screws and nuts are often used in drive mechanisms to adjust the relative positions of machine and tool parts. The lead screw provides robust but coarse adjustment of the relative positions of the parts. The nut is mount to the movable part and threadably driven by the lead screw. A problem exists, however, with such drive mechanisms in that a clearance space is created between the respective threads of the lead screw and driven nut which results in a degree of looseness therebetween that gives rise to an undesired backlash of the driven nut relative to the screw and thereby an unacceptable degree of imprecision in positioning the movable part.
Anti-backlash nuts and the like have been developed over the years to resolve this problem associated with such drive mechanisms. Representative examples of anti-backlash nuts are disclosed in U.S. Pat. Nos. 3,831,460; 3,977,269 and 4,434,677 to Linley, Jr. Each of the anti-backlash nuts of the Linley, Jr. patents discloses a nut construction which has internal threads thereon brought into close engagement with the lead screw threads to eliminate looseness and minimize clearance space between the driven nut and lead screw threads. While anti-backlash nuts like those of the Linley, Jr. patents appear to provide a satisfactory solution for backlash, they do not provide sufficiently fine or micro adjustment and positioning of movable machine and tool parts using lead screws in certain instances.
Certain precision equipment, such as computer disk drives, semiconductor tools and nanometer scales, require high-resolution positioning stages. Piezo actuators and flexure stages have been used for fine movements on top of existing linear crossed-roller or air-bearing stages. Use of second stages, however, limits the full travel of the existing stage, involves additional parts which add weight to and reduces surface area of the existing stage, adds height to the existing stage, and increases cost of the existing stage.
Consequently, a need remains for an innovation which provides a more effective solution for fine adjustment of precision equipment without introducing any new problems in place thereof.